I read that book end-to-end but an earlier edition than the current
one. Its mostly a book that lays out the principles and algorithms -
which are easy to specify for the front-end (as in DFA/LL1/LR1/LALR1)
but difficult to state for the backend. It doesn;t state the
implementation -but only states the principle which can be used in an
implementation.

> I really don't understand why the Dragon Book is considered canonical> for anything but parsing. Perhaps it's simply the incumbent. Anyhow,

It does explain some other things like I/M code optimization, 3
address form etc.. When I attended a post-grade course on compilers
(which essentially focuses on the back-end), the reading material was
mostly research papers. That is evidence that this book is indeed the
incumbent and we are left without a better choise:-).

Maybe the OP should read up GCC's online documentation and go through
its sources. That will give practical information for free.